Ores that are mined from the ground are obtained in a wide variety of sizes of particulates, varying from relatively small sizes to large chunks of mineralized material. The ore must be reduced to a size of particulate into a fine sieve range that is suitable for flotation where, through the use of suitable additives, the ore bearing particles are separated from the gangue.
One technique used by the mining industry to affect the requisite reduction in particulate size is to crush or grind the ore in a rotating grinding mill. As the mill rotates, the ore is lifted up by lifters and then dropped back onto itself. The impact causes the ore to be crushed, cracked, broken or otherwise formed into smaller particulates. Continued action in this manner causes a successive reduction in the size of the particulates which can be removed subsequent once a sufficiently small size has been achieved. The process is relatively continuous, with rough ore being fed at one end of the rotating mill and fine particulates being removed from the other.
In view of the abrasive character of the material being ground, the wear on the inside of the mill is a serious problem. Typically, such mills are lined with cast or wrought abrasion resistant ferrous alloy liners of several inches thick, or in some cases, with rubber or ceramic liners. These liners are typically in sections, with various configurations, usually being held in place by bolts which hold the liner tightly against the interior of the mill.
During service, the liners are worn by the abrasive action of the minerals being ground in the mill. The speed of wear can vary with a number of factors, including the nature of the ore bodies, which are typically irregular. Additionally, the configuration of the surface of the liner, during its service life, is an important consideration affecting both the life of the liner and the grinding efficiency or grinding rate of the mill. As a result, it is difficult to predict accurately the best time to replace the liners. Indeed, one problem with prior art mills is that in order to assess the current state of wear of the liners, the mill must be stopped, cleaned and a physical examination of the liners take place.
As commercial scale mills are quite large, and process many tons of ore per hour, regularly halting the process and cleaning the mill to determine the state of wear of the liners is impractical. Additionally, in cases of excessive liner wear, increasingly the abrasive particulate matter forms a slurry which races down the inside of the mill shell. Such slurry racing leads to greater abrasive forces being brought to bear on the inside of the mill shell, which can quickly lead to major damage of the mill shell.